| Message ID | 1414745252-4895-11-git-send-email-vincent.guittot@linaro.org |
|---|---|
| State | New |
| Headers | show |
On Fri, Oct 31, 2014 at 09:47:32AM +0100, Vincent Guittot wrote: > The call to arch_scale_frequency_capacity in the rt scheduling path might be > a concern for RT folks because I'm not sure whether we can rely on > arch_scale_freq_capacity to be short and efficient ? Well, you put it in quite a hot path on the CFS side too, so it had better be blazing fast anyhow. That said, can you move all the running + invariance bits at the beginning of the patch set, these appear to be the least controversial bits and 'desired' by quite a few people, so we'll try and get those agreed upon and merged first. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
On 3 November 2014 16:51, Peter Zijlstra <peterz@infradead.org> wrote: > On Fri, Oct 31, 2014 at 09:47:32AM +0100, Vincent Guittot wrote: >> The call to arch_scale_frequency_capacity in the rt scheduling path might be >> a concern for RT folks because I'm not sure whether we can rely on >> arch_scale_freq_capacity to be short and efficient ? > > Well, you put it in quite a hot path on the CFS side too, so it had > better be blazing fast anyhow. > > > That said, can you move all the running + invariance bits at the > beginning of the patch set, these appear to be the least controversial > bits and 'desired' by quite a few people, so we'll try and get those > agreed upon and merged first. ok I'm going to resend with the following order sched: add utilization_avg_contrib sched: Track group sched_entity usage contributions sched: remove frequency scaling from cpu_capacity sched: Make sched entity usage tracking scale-invariant sched: make scale_rt invariant with frequency sched: add per rq cpu_capacity_orig sched: get CPU's usage statistic sched: replace capacity_factor by usage sched: add SD_PREFER_SIBLING for SMT level sched: move cfs task on a CPU with higher capacity -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 31c3ec2..02e8f7f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5817,7 +5817,7 @@ unsigned long __weak arch_scale_cpu_capacity(struct sched_domain *sd, int cpu) static unsigned long scale_rt_capacity(int cpu) { struct rq *rq = cpu_rq(cpu); - u64 total, available, age_stamp, avg; + u64 total, used, age_stamp, avg; s64 delta; /* @@ -5833,19 +5833,12 @@ static unsigned long scale_rt_capacity(int cpu) total = sched_avg_period() + delta; - if (unlikely(total < avg)) { - /* Ensures that capacity won't end up being negative */ - available = 0; - } else { - available = total - avg; - } + used = div_u64(avg, total); - if (unlikely((s64)total < SCHED_CAPACITY_SCALE)) - total = SCHED_CAPACITY_SCALE; + if (likely(used < SCHED_CAPACITY_SCALE)) + return SCHED_CAPACITY_SCALE - used; - total >>= SCHED_CAPACITY_SHIFT; - - return div_u64(available, total); + return 1; } static void update_cpu_capacity(struct sched_domain *sd, int cpu) diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 7963981..8fd30c1 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1313,9 +1313,11 @@ static inline int hrtick_enabled(struct rq *rq) #ifdef CONFIG_SMP extern void sched_avg_update(struct rq *rq); +extern unsigned long arch_scale_freq_capacity(struct sched_domain *sd, int cpu); + static inline void sched_rt_avg_update(struct rq *rq, u64 rt_delta) { - rq->rt_avg += rt_delta; + rq->rt_avg += rt_delta * arch_scale_freq_capacity(NULL, cpu_of(rq)); sched_avg_update(rq); } #else
The average running time of RT tasks is used to estimate the remaining compute capacity for CFS tasks. This remaining capacity is the original capacity scaled down by a factor (aka scale_rt_capacity). This estimation of available capacity must also be invariant with frequency scaling. A frequency scaling factor is applied on the running time of the RT tasks for computing scale_rt_capacity. In sched_rt_avg_update, we scale the RT execution time like below: rq->rt_avg += rt_delta * arch_scale_freq_capacity() >> SCHED_CAPACITY_SHIFT Then, scale_rt_capacity can be summarized by: scale_rt_capacity = SCHED_CAPACITY_SCALE - ((rq->rt_avg << SCHED_CAPACITY_SHIFT) / period) We can optimize by removing right and left shift in the computation of rq->rt_avg and scale_rt_capacity The call to arch_scale_frequency_capacity in the rt scheduling path might be a concern for RT folks because I'm not sure whether we can rely on arch_scale_freq_capacity to be short and efficient ? Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> --- kernel/sched/fair.c | 17 +++++------------ kernel/sched/sched.h | 4 +++- 2 files changed, 8 insertions(+), 13 deletions(-)